Method and device for processing fermented milk products

ABSTRACT

The invention concerns a method for processing fermented milk products, in which the milk product passes through processing equipment executed with a plurality of openings from a retentate side toward a permeate side, in which the milk product is forced through the processing equipment with an insert feature preferably moved in a rotating arrangement along a retentate-side boundary surface of the processing equipment.

The invention concerns a method for processing fermented milk products,in which the milk product passes through processing equipment executedwith a plurality of openings directed from a retentate side toward apermeate side and a device that can be used to carry out such a method.

When fermenting milk, the soluble proteins of the milk are destabilizedduring the fermentation by the acid formed thereby. What is more, a geldevelops. To obtain end products with a desired appearance, a specifiedtexture and stability, it is necessary to crush this gel into small gelparticles in order to thus obtain a suspension or colloidal dispersionthat has the required product properties for a stirred yogurt, forinstance.

The mechanical crushing of the gel particles is usually performed bydirected agitation, pumping through slit openings or cloth sieves, orwith the aid of a sprocketed dispersion machine. A goal of thecorresponding processing of fermented milk products is to thereby obtainan end product with desired optical and sensory properties, such as anparticularly smooth end product. Thus the particle-size distribution ofthe gel particles resulting from crushing the gel has a great influenceon the texture, especially the consistency and the suspension stabilityof the end product.

The optimization of the desired product properties, such as obtaining aparticularly smooth end product and the maximum textural output, thatis, the optimum use of the fermented milk product, depends to a largeextent on the devices and method used to crush the gel particles. Withregard to the desired product properties, it is especially advantageousto adjust the particle-size distribution obtained to be as narrow aspossible by means of the processing and to select the largest possibleaverage particle size. At the same time, the average particle size isusually adjusted in a reasonable compromise between the desired productproperties (a smooth product) and textural output.

Using conventional methods and devices for crushing gel particles oftenleads to unsatisfactory product properties or to additional expenditureon milk proteins or binding agents. For example, end products are oftenobtained which occasionally contain optically visible gel particles. Inother cases, such as when using cloth sieves, non-uniform productproperties are observed due to blockages or surface film formation.

In view of the problems in prior art described above, the object of theinvention is based on making a method available for processing fermentedmilk products with which desired product properties can be attainedwithout excessive expenditure and on disclosing suitable devices forperforming the corresponding method.

This problem is resolved with regard to the invention by furtherdevelopment of the known method, which is essentially characterized bythe fact that the milk product is forced through the processingequipment with an insert feature, preferably moved in a rotatingarrangement along a retentate-side boundary surface of the processingequipment.

In the method according to the invention, small particles of thefermented milk product to be processed pass unimpeded through theopenings in the processing equipment, while large particles are gentlypressed by the insert feature through the openings in the processingequipment. At the same time, the openings are kept continuously free bythe movement of the insert feature along the retentate side. What ismore, the movement of the insert feature preferably takes places in arotating arrangement on the retentate side of the processing equipmentin order to maintain especially efficient cleaning of the openings inthe processing equipment.

The invention thereby originates from the discovery that the problemsthat are observed in prior art are attributed to too large ornon-uniform slit or pore widths or too high a mechanical stress on thegel particles. Surprisingly, it is found that through the use accordingto the invention of an insert feature movable along the retentate sideof the processing equipment, very much smaller pore sizes, compared tousing cloth sieves, are needed to attain the desired product propertiesand a smooth appearance, so that these desired properties can beobtained with a simultaneous guarantee of satisfactory textural output.

The combination according to the invention of the processing equipmentexhibiting openings permeable to fermented milk products with themechanical insert feature therefrom makes use of the fact that thefilter surface film usually occurring at filters or the sedimentationlayer or filter cake, with corresponding porosity and sedimentationresistance arising therefrom, are removed or stripped off, so that nofilter cake development occurs, and consequently only the geometry ofthe openings in the processing equipment affects the particle size anddistribution.

In the course of processing fermented milk products according to theinvention, the gel suspension obtained during the fermentation is forcedthrough the processing equipment. At the same time, the larger particlescollect at the openings and, due only to their lesser strength, areshoved through the openings with the aid of the insert feature and, thusdirected, are crushed In contrast to the known methods, the maximumparticle size can be affected by the method defined according to theinvention and the following advantages are presented.

Since the formation of the filter cake is counteracted, particlecrushing can be carried on continuously with constant quality forseveral hours without needing to replace or clean the processingequipment, because when using the insert feature, it does not lead tothe formation of a sedimentation layer, as occurs with the conventionalmethod. The maximum particle size can be especially adjusted through theselection of opening sizes in the specific processing equipment, and itcan be kept in continual operation for several hours. As a result, theaverage particle size can be maximized taking the sensory limits intoaccount, in order to thus also improve the possible manufacture ofmicrogel suspensions in the textural output with the method according tothe invention.

The energy input, the shear strength, and consequently the mechanicalload of the quite delicate gel particles are reduced by using an insertfeature according to the invention, so that more serum can be bound inthe individual particles and each individual gel particle consequentlyretains its maximum volume, which comes from gel formation during thefermentation. The spread of the particle-size distribution can bereduced, which leads to a more homogeneous suspension. This also has theresult that the maximum packing density of the suspension is reduced,which then leads to a higher viscosity. It also contributes toimprovement in the textural output.

In using the method according to the invention, optically visible and,under certain circumstances, larger particles perceptible to the senses,which appear with conventional methods, can be more dependably excluded.The stability of the suspension and of the end product is positivelyaffected, depending on the raw material. It is found, in comparison toconventional methods that, due to increased homogeneity of thesuspension and restriction in maximum particle size when using themethod according to the invention, that no perceptible sedimentation oflarger particles occurs in the end product.

With regard to the dependable detachment of particles being taken up onthe retentate side of the processing equipment while simultaneouslyavoiding excessive mechanical stress on these particles, it has provedto be favorable if the insert feature, in forming a wedge-shaped slit,which becomes narrower in a direction opposite to the movement of theinsert feature, is moved between a boundary surface of the insertfeature which faces the processing equipment and the retentate-sideboundary surface of the processing equipment along the retentate-sideboundary surface. In the course of this movement, the particles to beforced through the processing equipment come from an area with a largeslit width between the insert feature and the processing equipment inthe process of the insert feature moving into an area with a smallerslit width, so that upon reaching a slit at which a sufficiently largeforce is made available to the particles to force them through theopenings in the processing equipment, passage though the openings in theprocessing equipment results without more force being used for this thanis absolutely necessary.

With regard to dependably avoiding the formation of a filter cake on theprocessing equipment with a simultaneous guarantee of gentle treatmentof the fermented milk product to be processed, it has proved favorableif the retentate-side boundary surface of the processing equipment isswept at a frequency of 0.05 to 2 Hz, especially 0.1 to 1 Hz, by theinsert feature. Two or more insert elements of the insert feature canthereby each come into use at a lower frequency over the retentate-sideboundary surface of the processing equipment.

To obtain a homogeneous end product, it has proved favorable if theprocessing equipment exhibits a body, preferably rigid, executed with aplurality of openings of predetermined and geometry. Use of a rigid bodyas processing equipment executed with openings has the advantage thatspecified power ratios can be provided at the processing equipment bymeans of the crawler system of the insert feature, which help to avoidsubjecting the gel particles to excessive force. Within the framework ofthe invention, simple perforated plates, for example, can be used asprocessing equipment. With regard to obtaining more homogeneous productproperties, it has proved expedient if the openings in the processingequipment are executed in an essentially cruciform shape with uniformdiameter, in which the opening diameter can be 15 to 400 μm, especially30 to 200 μm.

As may be gathered from the preceding explanation of the methodaccording to the invention, a device according to the invention forcarrying out such a method is essentially distinguished by processingequipment permeable to fermented milk products from a retentate sidetoward a permeate side by virtue of it exhibiting an insert featuremovable along the retentate side and which forces the milk product in adirection toward the permeate side. At the same time, the insert featurecan include an insert element, which during movement along the retentateside forms a slit which becomes narrower in a direction opposite to thedirection of movement between a retentate-side boundary surface of theprocessing equipment and the insert feature.

But the processing equipment can exhibit a rigid body, such as aperforated plate executed with openings of predetermined size andgeometry, in which the openings can be executed in an essentiallycruciform shape with uniform diameter and the opening diameter is 15 to400 μm, especially 30 to 200 μm.

The invention is clarified below with reference to the drawings, towhich all the details essential to the invention and not furtherpresented in the description are explicitly referred. The drawings show:

FIG. 1 a schematic representation of a first embodiment of the inventionand

FIG. 2 a schematic representation of a second embodiment of theinvention.

In the embodiment of the invention depicted in FIG. 1, a fermented milkproduct is pumped from a supply container 10 through a pipe 12 in theflow direction indicated by the arrow P1 in a direction towardprocessing equipment in the form of a perforated plate 30 provided withpores. After passing the perforated plate 30, the fermented milk productgoes through the pipe 14 into a collection container 20. In theembodiment of the invention depicted in FIG. 1, the fermented milkproduct is forced through the perforated plate 30 with the aid of ainsert plate 40 movable in a rotating arrangement on the perforatedplate 30 in the [Translator's note: word(s) missing from the original]by the arrow P2. The insert plate 40 is so executed for this that awedge-shaped slit is formed, which becomes narrower in a directionopposite to the direction of movement P2 of the insert plate 40, betweenthe perforated plate 30 and the insert plate 40. A gentle processing ofthe fermented milk product is thereby favored, as has already beenexplained above.

In the embodiment of the invention depicted in FIG. 2, the fermentedmilk product is received in a supply receptacle 110, whose cylindricalsurface is formed by a filter basket 120. To process the fermented milkproduct, this is forced through the filter basket with the aid of aninsert plate 140 moved in a rotating arrangement along the insideboundary surface of the filter basket 120. Moreover, a shaft axis 145rotates the insert plate 140 in the direction designated by the arrowP2, such that a wedge-shaped slit is formed, which becomes narrower inthe direction opposite to the direction of movement of the insert plate140, between the insert plate 140 and the filter basket 120. Afterpassing the filter basket 120 the milk product also goes into a supplyreceptacle, which is not depicted in FIG. 2.

The invention is not limited to the embodiments depicted by thedrawings. Rather, it can also imagined, in using the insert feature,with two, three, or more insert plates, which could each be mounted ontoan insert shaft.

1. A method for processing fermented milk products, in which the milkproduct passes through processing equipment executed with a plurality ofopenings from a retentate side towards a permeate side, characterized bythe fact that the milk product is forced through the processingequipment by an insert feature moved in a rotating arrangement along aretentate-side boundary surface of the processing equipment.
 2. A methodaccording to claim 1, characterized by the fact that the insert feature,in forming a wedge-shaped slit, which becomes narrower in a directionopposite to the motion of the insert feature, is moved between aboundary surface of the insert feature which faces the processingequipment and the retentate-side boundary surface of the processingequipment along the retentate-side boundary surface.
 3. A methodaccording to claim 1, characterized by the fact that the retentate-sideboundary surface of the processing equipment is swept at a frequency of0.05 to 2 Hz, especially 0.1 to 1 Hz, by the insert feature.
 4. A methodaccording to claim 1, characterized by the fact that the processingequipment exhibits a body, preferably rigid, executed with a pluralityof openings of predetermined size and geometry.
 5. A method according toclaim 4, characterized by the fact that the openings are executed in anessentially cruciform shape with uniform diameter.
 6. A method accordingto claim 5, characterized by the fact that the opening diameter is 15 to400 μm, especially 30 to 200 μm.
 7. A device for carrying out a methodaccording to claim 1, with processing equipment permeable to fermentedmilk products from a retentate side toward a permeate side,characterized by an insert feature movable along the retentate side andthereby forcing the milk product in the direction of the permeate side.8. A device according to claim 7, characterized by the fact that theinsert feature exhibits an insert element, which during movement alongthe retentate side forms a slit, which becomes narrower in a directionopposite to the direction of movement, between a retentate-side boundarysurface of the processing equipment and the insert element.
 9. A deviceaccording to claim 7, characterized by the fact that the processingequipment exhibits a body, preferably rigid, executed with a pluralityof openings of predetermined size and geometry, especially designed inthe form of a perforated plate.
 10. A device according to claim 9,characterized by the fact that the openings are executed in anessentially cruciform shape with uniform diameter.
 11. A deviceaccording to claim 10, characterized by the fact that the openingdiameter is 15 to 400 μm, especially 30 to 200 μm.